Add argument to allow running compiler without sources

`-Xbuild-file` argument allows the compiler to run without
passing any Kotlin source file in arguments.
We have been using this property in
Kotlin Gradle plugin for a few important cases:
1. incremental compilation (to update caches when there are only removed files);
2. for KAPT (Kotlin sources don't make sense in context
of running APs).

We want to stop using `-Xbuild-file` in Kotlin Gradle plugin,
and avoid breaking the Gradle plugin or IC in other build-systems.

This change adds an argument to explicitly run
the compiler without specifying any Kotlin source file.

compiler/testData/cli/jvm/extraHelp.out

@@ -2,6 +2,7 @@ Usage: kotlinc-jvm <options> <source files>
 where advanced options include:
   -Xadd-modules=<module[,]>  Root modules to resolve in addition to the initial modules,
                              or all modules on the module path if <module> is ALL-MODULE-PATH
+  -Xallow-no-source-files    Allow no source files
   -Xassertions={always-enable|always-disable|jvm|legacy}
                              Assert calls behaviour
                              -Xassertions=always-enable:  enable, ignore jvm assertion settings;